Melamine

************From Wiki**************************

This article is about the chemical substance called melamine. The term "melamine" may also be used to refer to melamine resin, a plastic made from melamine and formaldehyde.
Not to be confused with melanin, a pigment found in skin and hair, or with melatonin, a naturally occurring hormone regulating the circadian rhythms of most animals.

Melamine is an organic base with the chemical formula C3H6N6, with the IUPAC name 1,3,5-triazine-2,4,6-triamine. It is only slightly soluble in water.

Melamine is a trimer of cyanamide. Like cyanamide, it is 66% nitrogen (by mass) and provides fire retardant properties to resin formulas by releasing nitrogen when burned or charred. Dicyandiamide (or cyanoguanidine), the dimer of cyanamide, is also used as a fire retardant.

Melamine is a metabolite of cyromazine, a pesticide. It is formed in the body of mammals who have ingested cyromazine.[2] It was also reported that cyromazine is converted to melamine in plants.[3][4]



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**Synthesis***************


Melamine was first synthesized by Liebig in 1834. In early production, first calcium cyanamide is converted into dicyandiamide, then heated above its melting temperature to produce melamine. However, today most industrial manufacturers use urea in the following reaction to produce melamine

6 (NH2)2CO → C3H6N6 + 6 NH3 + 3 CO2
It can be understood as two steps. First, urea decomposes into cyanic acid in an endothermic reaction (NH2)2CO → HCNO + NH3. Then cyanic acid polymerizes to form melamine and carbon dioxide: 6 HCNO → C3H6N6 + 3 CO2. The second reaction is exothermic and the overall process is endothermic.

The above reaction can be carried out by either of two methods:catalyzed gas-phase production or high pressure liquid-phase production. In one method, molten urea is introduced onto a fluidized bed with catalyst for reaction. Hot ammonia gas is also present to fluidize the bed and inhibit deammonization. The effluent then is cooled. Ammonia and carbon dioxide in the off-gas are separated from the melamine-containing slurry. The slurry is further concentrated and crystallized to yield melamine.[5] Major manufacturers and licensors such as DSM, BASF and Eurotecnica have developed some proprietary methods.

The off-gas contains large amounts of ammonia. Therefore melamine production is often integrated into urea production which uses ammonia as feedstock.

Crystallization and washing of melamine generates a considerable amount of waste water, which is a pollutant if discharged directly into the environment. The waste water may be concentrated into a solid (1.5-5% of the weight) for easier disposal. The solid may contain approximately 70% melamine, 23% oxytriazines (ammeline, ammelide and cyanuric acid), 0.7% polycondensates (melem, melam and melon).[6]


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